15 A Novel Membrane System for the Ultrafiltration of Oil Emulsions G. B. TANNY and A. KORIN Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: May 27, 1981 | doi: 10.1021/bk-1981-0154.ch015
Gelman Sciences, Inc., 600 S. Wagner Rd., Ann Arbor, MI 48106
The c o n c e n t r a t i o n o f emulsions is a s u b j e c t o f c o n s i d e r a b l e importance, encompassing the treatment o f industrial wastewater c o o l i n g or c u t t i n g f l u i d s ( 1 ) , the p r o c e s s i n g o f foods, and c e r t a i n pharmaceutical p r e p a r a t i o n s . When one takes i n t o cons i d e r a t i o n the increased use o f microemulsions(2), f u r t h e r growth in this area may be a n t i c i p a t e d . Ultrafiltration has q u i c k l y become the method o f choice f o r c a r r y i n g out t h i s pro cess (1), and in the past a r e p o r t has been made on the use o f a new c o n v e n t i o n a l thin-film composite UF membrane(3) t o accomplish t h i s g o a l . The present c o n t r i b u t i o n d e s c r i b e s a novel low pressure, high f l u x system which utilizes an "in situ" dynamically formed silica membrane particularly s u i t e d f o r the ultrafiltration of emulsions. The support f o r this s e l e c t i v e l a y e r o f silica was a p l e a t e d , t h i n channel c r o s s f l o w module(4) (tradename "Acroflux", Gelman Sciences, Inc.) c o n t a i n i n g 0.1 m o f 0.2 um pore size acrylonitrile copolymer membrane. This design c o n f i g u r a t i o n f o r flat sheet microporous membrane is relatively new and t h e r e f o r e bears d e s c r i p t i o n . Through the p l e a t i n g process one creates a p l e a t pack o f flow channels c o n s i s t i n g o f : (1) a cover channel m a t e r i a l ; ( 2 ) a t u r b u l e n t flow promoting spacer; and ( 3 ) the microporous membrane support. A cross s e c t i o n o f one o f these p l e a t e d channels is shown in Figure 1 a . The p l e a t pack is then arranged about a c e n t r a l d r a i n tube, glue seamed down the l o n g i t u d i n a l a x i s , and a s e a l r i n g is added t o prevent fluid bypass. A schematic o f the c a r t r i d g e in i t s housing is shown i n F i g u r e 1 b . Since the cover channel m a t e r i a l does not extend i n t o the glue s e a l s a t each end of the c a r t r i d g e , and is somewhat f r e e t o move, i t facilitates backwashing and is thus e s p e c i a l l y s u i t e d t o the membrane regene r a t i o n aspect o f dynamically formed membrane a p p l i c a t i o n s . In the s e c t i o n s which f o l l o w , we shall examine (a) the hydrodynamics o f this new module, (b) the formation and p r o p e r t i e s 2
0097-6156/81/0154-0237$05.50/0 © 1981 American Chemical Society
In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
238
MEMBRANES:
HF
AND
UF
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SYNTHETIC
Figure lb.
Schematic of an Aeroflux cartridge in a housing
In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
USES
15.
TANNY
AND
KORIN
239
UF of Oil Emulsions
of the s i l i c a dynamic membrane, and (c) i t s performance i n the module w i t h o i l / w a t e r emulsions under v a r i o u s c o n d i t i o n s .
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: May 27, 1981 | doi: 10.1021/bk-1981-0154.ch015
A.
Theory: Operation and Hydrodynamic A n a l y s i s o f the A e r o f l u x Module. The schematic cross s e c t i o n o f a s i n g l e p l e a t e d channel o f a u n i t mounted i n i t s housing i s shown i n F i g u r e 2. I n the case under c o n s i d e r a t i o n , the f l e x i b l e channel cover w a l l m a t e r i a l i s impermeable to flow and a l l the space between i t and the w a l l o f the housing becomes p r e s s u r i z e d to Pp, the feed entrance pressure. Thus, at any p o i n t w i t h i n the l e n g t h o f the channel, a pressure drop, Pp-P(x), e x i s t s both along the channel and across the channel cover w a l l . T h i s pressure drop helps to seat the channel cover w a l l on the spacer and maintain channel dimensions. (On the other hand, during the b a c k f l u s h o p e r a t i o n , the channel cover w a l l i s somewhat f r e e to move away from the spacer to f a c i l i t a t e c l e a n i n g . ) Let us consider the mass and f o r c e balance i n an e l e ment dx along the channel. Assuming u n i t a r y w i d t h , the change i n the flow r a t e , dQ, i s given by:
-dQ =
P(x) - P ^ m
(1)
dx
The change i n pressure down the channel element dx i s given by the equation (JL): -dP = aQ
n
over
the same
(2)
dx
where "a" i s the constant r e f l e c t i n g the f r i c t i o n and height of the spacer ( i d e n t i c a l to that o f the channel) and "n" i s a constant, w i t h the values n = 1, f o r laminar flow, and n = 2 , f o r t u r b u l e n t flow. Combining equations ( 1 ) and ( 2 ) y i e l d s : dQ
_ J
=
dP
aR
L_
m
n
(
3 )
K D J
n Q
Rearranging and i n t e g r a t i n g t o the a p p r o p r i a t e boundary c o n d i t i o n s , one o b t a i n s : ( n Q
d Q
=
_ L
/
( _ P
P p
)
d
P
In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
(4)
SYNTHETIC
MEMBRANES:
HF
AND
UF
USES
This equation can now be used to o b t a i n the f o l l o w i n g r e l a t i o n s h i p s between the e x p e r i m e n t a l l y r e l e v a n t f a c t o r s , A p^, the t o t a l trans-channel pressure drop, A P , the average opQ e r a t i n g pressure ,Q, the permeation r a t e , and X = — : (see Appendix No. 1 ) . P 1. For the t u r b u l e n t flow c o n d i t i o n : R
,1/2
A
3/2
-(f)
Y Q
( 5 )
p
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: May 27, 1981 | doi: 10.1021/bk-1981-0154.ch015
where Z = 1/3 [ ( 1 + X )
3
(6)
3
-X ]
m A
Y
= 1-
P
R
-=
(8)
2AP APm
and
= R 0 m P
(9)
p
m
These r e l a t i o n s can be used t o generate the d i a gram i n F i g u r e 3 , which d e f i n e s the a n t i c i p a t e d range o f pressure drop and average pressure necessary t o achieve any d e s i r e d permeation r a t e a t some d e s i r e d r a t i o o f r e t e n t a t e to permeation flow r a t e . For laminar flow c o n d i t i o n s
2.
/ s \ A P
where
C
=
(2k)
1 / 2
1/2 < Y
